This invention relates to control circuits for gas discharge lamps. The invention is especially adapted for fluorescent lamp control circuits.
Low-cost control circuits for powering fluorescent lamps from low voltage DC power sources are well-known. Such circuits typically maintain an AC current through a pair of fluorescent lamps, once the lamps are in a conductive state, and produce a high voltage between opposite filaments of the fluorescent lamps to ignite the fluorescent lamp if it is not in a conductive state.
One problem with such known control circuits for fluorescent lamps is that, if one of the fluorescent lamps is not properly seated in its socket, or if a lamp becomes leaky and thus contaminated with air, the high voltage cannot ignite the lamp. This causes the high voltage to continue to rise and may result in arcing and corona discharge in the control circuit, which may destroy or significantly limit the life of the control circuit. While some forms of protection of the control circuit would be apparent to the skilled artisan, such as the use of a metal oxide varistor or zener diode across the terminals producing the high voltage, such form of protection would not be satisfactory. In order to provide protection, the power requirements of such protection devices would be very large and their expense prohibitive for a low-cost supply.